1. Field of the Invention
This invention relates to electrolyte solvents and more specifically, this invention relates to a method for producing high voltage electrolyte solvents for batteries.
2. Background of the Invention
Carbon-fluorine bonds are among the strongest in organic chemistry, having an average bond energy of approximately 480 kJ/mol. As such, fluorinated organic compounds have high thermal, chemical, and electrochemical stability. It is this stability that makes such compounds preferred solvents for electrolytes used in high voltage batteries. Currently used electrolyte solvents do not perform well in high voltage lithium ion battery applications.
State of the art methods for making electrolyte solvents typically require severe reactants and reaction conditions. For example, in protocols for producing fluorinated carbonate solvents, phosgene and triphosgene are sometimes utilized. Other processes utilize hexachloroacetone to provide the carbonyl moiety. Chlorinated reagents are particularly troublesome inasmuch as chlorine wreaks havoc with battery chemistry. Therefore, elaborate distillation and purification steps are required to remove any traces of chlorine, and particularly chloride ions, from final electrolyte solvent produced.
The toxic reagents utilized in state of the art methods hinder commercialization. The methods are highly inefficient (30-40 percent yields) and require additional aqueous treatments to remove byproducts and residual reagents. This results in the generation of significant amounts of waste.
Prior art methods for producing the carbonated solvents often require internal temperatures of 100° C. maintained for 20 hours or more.
Furthermore, purification of fluorinated carbonate solvents is a difficult distillation, requiring a spinning column. This is because azeotropic mixtures may be formed between the formed solvent product and the aforementioned reaction solvents. (When azeotropic mixtures are boiled, the condensate has the same proportions of constituents as the pot mixture. As such, constituents cannot be separated via distillation.)
Also, state of the art methods for producing the electrolyte solvents often require strictly anhydrous reaction conditions. As such, nitrogen-filled gloveboxes are required. Overall, this results in a process that is too costly and too cumbersome to be commercially viable.
In light of the foregoing drawbacks, state of the art methods for producing electrolyte solvents often need to be conducted in controlled atmospheres (e.g., glove boxes). These processes typically require 8-12 hours for completion.
A need exists in the art for a method for economically producing electrolyte solvent, such as bis(trifluoroethyl) carbonate and trifluoropropylene carbonate, particularly for use in Li-ion battery electrolyte production. The method should use relatively mild reactants and require relatively low temperatures. The method should not require special reaction atmospheres. Also, the method should minimize waste streams. Lastly, the method should require no more than four hours, and preferably between about 1 and 4 hours.